MiG-21Bis and Bis-B FM Mods

[Svetlin 543]

Can you post also the first part of table 28 and probably the next page after this table, as looking at this part of the table alone, I cannot figure out the meaning of PX, X, P, У and PУ.

I think I can help with the translation of the rest.

 

Chapter VII - Weight and balancing characteristics

Table 28 continued

===============

Table headers:

Name / PX (measured in kg) / X (measured in meters) / P (measured in kg) / У (measured in meters) / PУ (measured in kg)

==============

Under the wings

==============

Inner pylons loadout

==============

R-2R missiles loaded (2 pcs)

--------------------------------------------

pylon BDZ-60-21D

launch rail APU-13U

R-3R missiles

==============

R-55 missiles loaded (2 pcs)

-------------------------------------------

pylon BDZ-60-21D

launch rail APU-68UME

R-55 missiles

===============

R-13M missiles loaded (2 pcs)

--------------------------------------------

pylon BDZ-60-21D

launch rail APU-13MT

R-13M missiles

==============

UB-16 rocket pods loaded (2 pcs)

--------------------------------------------

C-5M unguided rockets (16 * 2)

rocket pods UB-16-57UMP

pylon BDZ-60-21D

===============

OFAB-100 bombs loaded (2 pcs)

---------------------------------------------

pylon BDZ-60-21D

bombs OFAB-100

===============

Unguided missiles S-24 loaded (2 pcs)

---------------------------------------------

pylon BDZ-60-21D

launch rail APU-68UME

unguided missiles S-24

===============

OFAB-250 bombs loaded (2 pcs)

---------------------------------------------

pylon BDZ-60-21D

bombs OFAB-250

===============

UB-32 rocket pods loaded (2 pcs)

--------------------------------------------

pylon BDZ-60-21D

rocket pods UB-32A

C-5M unguided rockets (2 * 32 pcs)

===============

Incinerating canisters ZB-500 loaded (2 pcs)

-------------------------------------------

pylon BDZ-50-21D

ZB-500 incinerating canisters (from me - something like napalm bombs I guess)

================

 

By the looks of it, the table shows parameters with various types of weapons loaded, giving first total amounts for the whole unit loaded under the wing (weapon+pylon+launch rail) and then giving a break-down for each component - the weapon alone, the pylon alone, the missile rail alone (if one is needed for the weapon; naturally no missile rails needed for bombs and rocket pods). Hope that helps.

Edited August 15, 2019 by Svetlin

[+baffmeister 1,205]

Thanks Svetlin. This page looks like the introduction for the weight and balance section I've posted:

This page has some info on the 490 liter drop tanks at the bottom of the page:

There is another page that I haven't posted that shows information for the 800 liter centerline drop tank. Not sure when that tank became available and what MiG-21 versions it fits but it might be a nice add-on project for someone. ThirdWire only made the 490 liter version.

 

[Svetlin 543]

Hi, I will translate these for you as well, but after a quick glance at the 2 pages, I still cannot make out what PX, X, P, У and PУ mean.

As for the 800L drop tank, that could be loaded under the fuselage, from what I have read at www.airwar.ru, the tank was first introduced on the MiG-21SM (first flight in 1967) and was available on all subsequent variants such as SMT, M, MF, bis.

I am not 100% sure, but I am willing to believe that the subject 800L drop tank was later used also on the MiG-23 and we do have that tank stock in SF2.

In fact I have modified the MiG-21s in my install to carry the MiG-23 800L drop tank and it fits quite nicely, here is a proof of concept 

Edited August 17, 2019 by Svetlin

[Svetlin 543]

OK, now here goes the first page:

Aircraft Weight Summary

In order to calculate the balance of the aircraft at the possible changes in aircraft construction and equipment, the weight and center of weight of various aircraft equipment and systems are listed. Aircraft balance calculations are performed using the X and Y axis. Axis X is the aircraft longitudinal axis and matches the aircraft constructional horizon. The Y axis is perpendicular to the X axis and is vertical, situated 600 mm towards the aircraft tail from frame #16. The point where axis X crosses axis Y is the starting point in the center of weight position calculations for the aircraft, its systems and each component, which is part of the various aircraft systems. The coordinates of systems and components, situated in the direction of the aircraft tail on the X axis and up vertically on the Y axis, have a "+" sign and those towards the aircraft nose on the X axis and down vertically on the Y axis have a "-" sign.

(Picture 92 shows the location of the balancing axis)

Weight summary and load balance and the main equipment with respect to the centering axis are listed in table 27.

Weight summary and balancing of loadout with respect to the centering axis are listed in table 28.

Weight Summary and load balance and main equipment

Table 27

===============

Table headers:

Name / PX (measured in kg) / X (measured in meters) / P (measured in kg) / У (measured in meters) / PУ (measured in kg)

==============

Aircraft with normal load (landing gear is lowered position)

Empty aircraft

Normal load

Normal load

Pilot with parachute

R-3R missiles (2 pcs)

Cartidges (250 pcs)

Fuel in fuel tank #2 V = 830L

Fuel in fuel tank #3 V = 340L

Fuel in fuel tank #4 V = 175L

Fuel in fuel tank #5 V = 245L

Fuel in fuel tank #6 V = 185L

Fuel in the front wing tanks V = 360L

Fuel in the rear wing tanks V = 220L

Fuel in the fuel tank on the aircraft back (in the structure behind the canopy that flows into the aircraft vertical tail) V = 530L

Launch rail APU-13U-2 (2 pcs)

==============================

The other page will follow probably tomorrow.

[+baffmeister 1,205]

It might be starting to make some sense. Using column P, the aircraft empty weight is 5843kg,  2883KG is the full internal fuel+pilot+missiles etc, and 8726kg is the sum of the parts.  That's important because now I know which column to look under to get the weight of various racks etc. X and Y columns, as you mentioned, are the length of the horizontal and vertical arm, in meters, from the center reference point. PX and PY might be the resulting moment of the weight times the arm but that doesn't seem to quite work out. Using the two 490liter drop tanks the chart shows 940KG under P column for the mounted tanks and an arm of +1.34M under the X column. If I multiply those together I get a moment of 1259.6KG which is close to the 1257KG under the PX column but, not exactly.

Anyway, that's been a big help! 

Edited August 18, 2019 by baffmeister
mistake

[+baffmeister 1,205]

After looking through the rack weights it looks like there is some room to save some weight. Keeping in mind the posted documents show the weight for 2 racks, they seem to average around 30-35KG each, with some variation probably due to additional hardware required for certain weapons. ThirdWire is using 60KG for each main rack. On the other hand, the weight of the missile rails from the document are heavier than the 25kg used in the ThirdWire data but overall, with a full loadout, the weight reduction would be around 100kg.

I checked the fuel plus tank weights for the 490L and 800L tanks and the ThirdWire tank+fuel is lighter than the document weights but the document info indicates a bit more fuel available. For the next update I will probably leave the tank weight/capacities as is but will include Svetlin's idea of using the 800L MiG-23 on the center pylon. It does look like the correct tank, from the diagrams in the document.

Svetlin, I don't need any more translations for the previous documents but could you take a look at this one? I'm checking the deflection angles for the control surfaces and the TW rudder and ailerons match the documents but the H-Stab is different. I'm quite sure the red box I outlined is for the H-Stab but I'm curious about the statement underlined in yellow:

For anyone interested, here's the info, at the bottom, for the 800L centerline tank.  The way the fuel weight is divided might indicated the 490 and 800 liter tanks had 2 compartments:

[Svetlin 543]

Hi, my pleasure, here it goes.

 

Chapter II - Geometrical data

Horizontal tails

a) moving surface

Area

Mean aerodynamic chord (MAC) of the moving part of the horizontal tails

- along the air flow

- perpendicular to the rotation axis

Spread

Sweep angle at 1/4 MAC

Elongation

Waist

Cross angle V

Relative thickness (along the air flow)

Profile along the air flow

Horizontal tail shoulder (distance from wing 0.32 MAC to 0.25 MAC of the moving part of the horizontal tail)

=======================================================

Here is the part you are interested in:

Deflection angles along the air flow (maximum angles at high level setting of the automatic booster control)

- front part of the stabilizer turned up

- front part of the stabilizer turned down

Sweep angle of the stabilizer rotation axis

Location of the rotation axis in % from the MAC of the moving part of the horizontal tail

========================================================

b) with ventral fin

Area

Spread

Mean aerodynamic chord along the flow

 

Vertical tail (fin)

(without the ventral fin)

Area of the vertical tail

Mean aerodynamic chord

Sweep angle along 1/4 MAC

Elongation

Waist

Relative thickness of the vertical tail (mean or average)

Profile along the air flow

Vertical tail shoulder (distance from wing 0.32 MAC to 0.25 MAC of the vertical tail)

Rudder area

Rudder mean aerodynamic chord (perpendicular to the rotation axis)

Area of the axial compensation of the rudder (in % of the rudder area)

Maximum rudder deflection angle (perpendicular to the rotation axis)

 

I must ask you to excuse me as my translation is that of an amateur. I have no technical education and I have only read about most of the technical terms used here, but only in Russian and Bulgarian, so I believe I understand what most of these terms mean, yet my lack of experience with the English terms is rather obvious. So I just hope you are able to make something out of what I am trying to translate as I am sure I am not using the proper English term in most cases.

[+baffmeister 1,205]

Your translations are good, thank you!

[MigBuster 2,884]

I pinged Topolo a message who is the author of many of the HFFM flight models over the years and has done quite a bit of work on aerodynamically modelling the MiG-21s as well and he does confirm that Emergency Reheat value is not static zero airspeed but exactly as that Bis manual states at M1 SL.

 

 

 

[Stratos 3,188]

While searching for proper schemes for 1982 Bekaa 21Bis, I found this story, not sure is true, but at least is interesting. MiG-21 doing Pugachev Cobra ( shoudln't the engine flame??)

https://nationalinterest.org/blog/buzz/unknown-story-syrian-mig-21-pilot-who-developed-cobra-maneuver-72081

specially this part...

Mohammed’s initial solution was based on Soviet manuals and consisted of rapid descending turns followed by a sudden activation of the afterburner and a climb. However, in the course of one of related test-flights, in early 1967, Mohammad inadvertently pitched the nose of his MiG too hard, so that the forward movement of his aircraft nearly stopped. When he engaged the afterburner his MiG ended ‘standing on its tail’, with the nose pointing almost vertically into the sky, on the verge of flipping out of control. Mohammad recovered on time to prevent a crash, but it was a close call: in order to prevent this from happening again, he decided to try flying the same manoeuvre after engaging the afterburner, so to enable the engine to spool up on time (the Tumansky R-11 was notorious for its slow reaction to throttle movement).

 

That was the moment that what later became known as the ‘zero speed manoeuvre’ was born.

[MigBuster 2,884]

in 67 they were flying different MiGs with different engines if you are referring to the DCS Bis - which according to all the Bis pilots that test flew and verified the DCS FM the engine flames out as soon as there is much in the way of negative G especially at low speeds as soon as the nose goes forward. 

That doesn't sound like a cobra........the aircraft that have done that (Su-27 etc) still had some directional stability, likely pitched up to a far higher transient AoA and still appear to be in control and flying when the nose came down.

 

[Stratos 3,188]

No not DCS Bis, I'm refering to the real bird, and our MiGs too.

[Stratos 3,188]

BTW, is always interesting to read about new MiG tactics against the Mirage III for 1966-73 timeframe.

[jeanba 1,920]

Topolo on checksix forum extrapolated from fligh manuals comparisons between various planes of the 60s 70s :

http://www.checksix-fr.com/documentation-performances-f-5e-mig-21-mirage-iii-f-4/

Globally, the Mirage III is outclassed by the Mig21bis except in manuevrability below 15000 ft

 

[Stratos 3,188]

Jeanba, thanks for that, curious how close those two planes were. Any MiG-21 expert can explain his tactics here?

[jeanba 1,920]

What do you mean ?

No tactics here

Topolo's work is an estimate of performances based an available Flight Manual.

The data and curves were then converted and adapted to a format which made them easier to compare under the NATOPS framework

[Stratos 3,188]

I haven't expressed properly, I mean, how you fly in a MiG-21 in dogfight, which tactics do you use?

[jeanba 1,920]

As far as I am concerned : Boom & Zoom, vertical plane, high subsonic, high altitude

Avoid Dogfight, missile attack mainly.

Be carefull of improved IRM missiles such as AIM-9D or Shafrir II, compared to AIM9B

The only time I make hard maneuver is to avoid being in the missile arc.

 

I fight in Early VN environments, Six days War (early migs), Yom-Kippur (Mig21MF) and Ogaden (vs F5s or even otehr Migs 21)

Edited September 16, 2019 by jeanba

[+baffmeister 1,205]

I agree with jeanba. I still think there is some room to improve the low speed performance of the TW MiG-21 but in general you want to keep the speed up. Better, and I think more realistic low speed behavior would improve the defensive capabilities as well as improve the potential for firing solutions during lower speed turns but only in certain situations.

I've been trying a few things with the Bis FM to better match the low speed behavior as described in the flight manual but it involves too much conjecture at this point. I'm still taking a look at the charts from the CheckSix site but I need more data to test against before releasing anything.

From the flight manual, it seems the MiG-21 can easily get into the higher alpha zone while the TW MiG-21 FM tends to get "stuck" at about 28deg AOA. There seems to be a number of reasons for that. TW modeled quite a bit of nose down pitch moment in the stall region and the lift distribution is almost 70% on the outer/aft wing panel which makes it more difficult to get the nose up at low speeds. It will take some research and a lot of testing to see what might be improved regarding the low speed/higher alpha performance.

[jeanba 1,920]

I think  that low speed fight in SF2 is very dangerous, especially when you are outnumbered :

It seems  AI is very good at coordinating attacks from several direction, and I was often shot down by an unseen attacker :

"A Mirage in your six is better than no Mirage at all"

 

Edited September 17, 2019 by jeanba

[Stratos 3,188]

Should the Bis carry flares or not? DCS one has them, but I cannot even add them to my Bis!

 

Got it!

 

[+Crusader 2,101]

The MiG-21 units in Afghanistan received flare launchers. To counter the Stinger threat.

Afghan Air Force units too, theres a good photo of a PFM somewhere.

[+baffmeister 1,205]

Life in the Danger Zone:

I followed that guy around for about 10 minutes trying to get get an awesome high alpha Aphid launch screen shot but the new higher AoA capability is proving to be quite useless during dog fights. The speed loss is very rapid and any potential firing solution is gone in an instant. I was down to about 135kts when I took the screen shot. The higher AoA is sometimes useful for defensive purposes if you have a stubborn EA on the tail. The rapid speed loss can force an overshoot but the sink rate gets very high at idle power and low speed so altitude must be carefully watched.

After messing up the first attempt at a Bis FM update I going to change this project to a general review and potential updates for all the MiG-21's. I think the weapon rack weight adjustments are useful and a new 800L centerline drop tank would be nice. The MiG-23 800L "stand in" is good for now but it has an oval shape and conflicts a bit with the MiG-21 landing gear doors.

I found an interesting document on basic delta wing aerodynamics so I settled on an approach to use for the modified FM. I won't get into details at this point but it involves transferring lift from the outer aft to the inner forward wing panel to model the vortex break down which moves from aft/outboard to forward/inboard. According to the document, the vortex breakdown starts in the 20-25 deg AoA range.

Still some testing to do but should have a Bis test FM ready before year end. Will also include a modified FM for the MiG-21F. It's over 1000kg/2200lbs lighter than the Bis so might be more effective at high AoA. Or not.

 

[+baffmeister 1,205]

Test FM's for the two ThirdWire MiG-21Bis models attached at the bottom. The main objective with these is to try and model the high alpha behavior as described in the flight manual. I had to make way more changes than expected to add only about 5degs to the existing AoA range. 

With the revised FM's I'm trying to model some lift transfer from the outer to inner wing panels. According to a document I read this occurs in the 20-25 deg range. To get a smoother transfer I went with the low end of the range at 20deg. The edits to the outer wing panel limit the CLmax to what it would be at 20deg, based on a straight line variation. The "surplus" CLmax has been added to the inner/forward wing panel that has a revised stalling angle of 20deg, so it transitions to the CLmax slope at 20deg and continues up to a new AlphaMax of 33deg, versus the original at 27.66deg. Some additional CLmax has been added to model the added lift available at 33deg. Some additional edits were required to the StallMoments and the StallXACShift tables to reach the higher AoA range.

Here's a description of the idle power level flight stall behavior at 5000m/16400ft from the Bis flight manual, with some comments regarding the revised FM's in brackets:

340-370kmh /184-200kts: pre stall buffeting [around 170-175kts]

280kmh / 151kts: Aileron deterioration [somewhat noticeable]

230-240kmh / 124-130kts: Wing rock develops but pitch stable [no noticeable wing rock]

220-230kmh / 119-124kts: Aircraft starts to pancake [ I assume that means a high sink rate but pitch stable, which it does]

200kmh / 108kts: Large wing rock up to 50deg left/right at about 6-10deg sec [ Nope! ]

I did some back to back testing with the stock and revised FM's and the sustained G remains about the same but the revised FM generates a higher instantaneous G due to the increased lift available at 33deg.

The only way I found to check the low speed behavior was some calculated data from the CheckSix website. The test involved a very low speed turn at mach 0.22 / 133ktsIAS at 5000ft with two R-60's and 50% internal fuel. It was quite difficult to fly accurately but the best results were within +-2sec of the calculated data. The calculated data is 52sec for a 360deg turn. [6.9deg/sec]

Some additional edits from the flight manual:

Gear limit speed: quite high at 600kmh / 324kts. The sop's for landing call for gear down first at 550kmh/297kts then approach flap at 500kmh/270kts with full flap selected at 400-420kmh / 227kts.

Flap limit speed: Not even mentioned in the flight manual and no description of the "floating flap" system! I based the flap1 speed on the sop's and the flap2 speed is the TW original.

The rack weights have been adjusted using the info from the technical manual and the MiG-23 800L tank has been added as an option.

Recommended take off rotation angle is 11-13deg. The manual calls for early aft stick, maybe due to ground effect issues, but I find 130-150kts, depending on weight, and 13deg AoA gives a nice lift off at the proper speed.

Typical approach speeds at light weight are quite high at 180kts but that's probably due to over the nose visibility issues. The target touch down speed is considerably lower at 150kts.

The canopy works with Shift0[zero]

I've found the additional AoA range quite useless during dogfights due to the rapid speed loss. It's sometimes useful for evasive maneuvering but that's really a last chance maneuver, it's better to keep the speed up.

An interesting document here describing the U.S. tests on a MiG-21F. https://theaviationist.com/wp-content/uploads/2013/11/havedoughnut.pdf

I have read some other documents describing how skilled U.S. aggressor pilots could trick the rookies into low speed turn and burn dogfights with the MiG-21's and F-5E's but once the lesson was learned the results were much different so better not to go there. Even the ThirdWire AI will be flying rings around you!

Revised FM's here: MiG21bisFMs0.96.zip

I'm going to modify the light weight MiG-21F as well, it should be ready soon.

 

 

[+Coupi 4,388]

Hello,

In the previous v0.95 you have added an emergency thrust with the Tumanskiy R-25-300 (MiG-21bis Late).

In your v0.96 these data were deleted. Is it volontary ? 

Very good stuff !!! 

Edit : thank you for the MiG-21F doc very interesting !

Coupi.

Edited January 5, 2020 by Coupi